Method and apparatus for producing double-walled containers

Abstract

A method and apparatus for the formation of double-walled containers with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, stretch-blow moulded as single bodies out of thermoplastic material, and suitable for mass-production. A thermoplastic tubular blank is formed and then heat-conditioned. The heat-conditioned tubular blank is then mechanically stretched longitudinally and blow-formed outwards by gas pressure to conformingly and stretchingly assume the tubular blank to the shape of a first dual-container shaped mould cavity set in order to form a stretch-blow moulded first container integrally connected to a second container, with both containers extending in opposite directions. Next, additional heat-conditioning is applied to further heat-condition as necessary the stretch-blow moulded second container and if deemed an advantage, at least part of the first container. Then at least one profiled inversion piston and a second dual-container shaped mould cavity set are provided along with one or more wall stability devices applied to at least part of the wall surface(s) of either or both of the two integrally connected stretch-blow moulded containers, such that the second container side wall(s) may be inverted at least partially inside-out, while at the same time the second container bottom wall at least substantially does not invert, in order for the second container to become a substantially mirror-image inverted second container extending in the same direction as the first container, and an air gap is formed between the first container and second container.

What is claimed is: 
     
       1. A method for producing a double-walled container with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, the method comprising the steps of:
 providing a first mould with a first mould cavity having a dual-container shape; 
 providing a below melt-temperature thermoplastic tubular blank with an open first end and an opposite second end, the blank having an initial blank length L0 and an RSmax lower than 3, where RSmax is herein defined as the largest value of RS occurring along the length of the tubular blank and Radial Stretch ratio RS is herein defined as the ratio between a circumference at any point after pressure stretching and the corresponding circumference of the original tubular blank; 
 heat-conditioning the tubular blank to a first heat-conditioned temperature within a heat-softened temperature range but below the melt temperature of the thermoplastic material; 
 placing the heat-conditioned tubular blank inside the first dual-container shaped mould cavity; 
 applying a mechanical blank stretcher to mechanically stretch the heat-conditioned tubular blank in a longitudinal axis direction to a stretched length L1, such that the Longitudinal Stretch ratio LS, herein defined as the ratio L1/L0, is larger than 1; 
 blow-forming the longitudinally stretched tubular blank outwards by gas pressure in order to conform the longitudinally stretched tubular blank to the first mould cavity such that the maximal stretch-blow mould ratio RLmax, herein defined as the ratio between RSmax and LS, is lower than 3 and preferably substantially 1 or less; 
 to obtain as an intermediate product a stretch-blow moulded integral dual-container with the structure of a first container and an integrally connected second container, with the first container and second container extending in opposite directions from each other, wherein said second end of the tubular blank forms a bottom portion of the second container; and then: 
 inverting the second container such that it extends in the same direction as the first container; 
 to obtain as an end product a stretch-blow moulded integral double-walled container with the structure of a first container and integrally connected second container extending in the same direction with an air gap between the first container and second container; 
 wherein said inverting of the second container is performed by 
 providing at least one profiled inversion piston capable of being displaced in the longitudinal direction of a second dual-container shaped mould cavity; 
 engaging the at least partial bottom wall of the heat-conditioned second container with the at least one provided inversion piston; and 
 displacing the at least one profiled inversion piston in the longitudinal direction of the second dual-container shaped mould cavity such as to displace the at least partial bottom wall of the heat-conditioned second container toward and into the first container, wherein a side wall of the heat-conditioned second container is inverted progressively with progression of the displacement of the bottom wall of the heat-conditioned second container. 
 
     
     
       2. The method according to  claim 1 , further comprising, before the step of inverting the second container, the step of:
 heat-conditioning the stretch-blow moulded integral dual-container in any relevant region or regions of the first container and/or second container to a second heat-conditioned temperature; 
 wherein the step of inverting the second container is executed while the stretch-blow moulded integral dual-container is in a heat-conditioned state. 
 
     
     
       3. The method according to  claim 1 , further comprising the steps of:
 providing a second mould with a second mould cavity having a dual-container shape; 
 placing the stretch-blow moulded integral dual-container inside the second dual-container shaped mould cavity; 
 
       wherein the step of inverting the second container is executed while the stretch-blow moulded integral dual-container is inside the second dual-container shaped mould cavity. 
     
     
       4. The method according to  claim 1 , wherein the step of heat-conditioning the stretch-blow moulded integral dual-container is executed either prior to insertion into the second dual-container shaped mould cavity, while inside the second dual-container shaped mould cavity, or both. 
     
     
       5. The method according to  claim 1 , further comprising the step of manually inverting the second container. 
     
     
       6. The method according to  claim 1 , wherein said second end of the tubular blank is closed. 
     
     
       7. The method according to  claim 1 , wherein said second end of the tubular blank is open. 
     
     
       8. The method for producing a double-walled container with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, the method comprising the steps of:
 providing a first mould with a first mould cavity having a dual-container shape; 
 providing a below melt-temperature thermoplastic tubular blank with an open first end and an opposite second end, the blank having an initial blank length L0 and an RSmax lower than 3, where RSmax is herein defined as the largest value of RS occurring along the length of the tubular blank and Radial Stretch ratio RS is herein defined as the ratio between a circumference at any point after pressure stretching and the corresponding circumference of the original tubular blank; 
 heat-conditioning the tubular blank to a first heat-conditioned temperature within a heat-softened temperature range but below the melt temperature of the thermoplastic material; 
 placing the heat-conditioned tubular blank inside the first dual-container shaped mould cavity; 
 applying a mechanical blank stretcher to mechanically stretch the heat-conditioned tubular blank in a longitudinal axis direction to a stretched length L1, such that the Longitudinal Stretch ratio LS, herein defined as the ratio L1/L0, is larger than 1; 
 blow-forming the longitudinally stretched tubular blank outwards by gas pressure in order to conform the longitudinally stretched tubular blank to the first mould cavity such that the maximal stretch-blow mould ratio RLmax, herein defined as the ratio between RSmax and LS, is lower than 3 and preferably substantially 1 or less; 
 to obtain as an intermediate product a stretch-blow moulded integral dual-container with the structure of a first container and an integrally connected second container, with the first container and second container extending in opposite directions from each other, wherein said second end of the tubular blank forms a bottom portion of the second container; and then: 
 inverting the second container such that it extends in the same direction as the first container; 
 
       to obtain as an end product a stretch-blow moulded integral double-walled container with the structure of a first container and integrally connected second container extending in the same direction with an air gap between the first container and second container; and 
       stabilising a side wall of the first container and/or second container during the step of inverting the second container. 
     
     
       9. The method according to  claim 8 , wherein the step of stabilising a side wall of the first container and/or second container comprises the step of applying higher than atmospheric air pressure interior to at least one integrally connected pressure chamber and/or the dual-container mould cavity in order to provide a higher than atmospheric air pressure interior to the stretch-blow moulded integral dual-container during inversion. 
     
     
       10. The method according to  claim 8 , wherein the step of stabilising a side wall of the first container and/or second container comprises the step of applying lower than atmospheric air pressure via the dual-container mould cavity to any one or more exterior surfaces of the stretch-blow moulded integral dual-container in the region or regions where wall stability control is required. 
     
     
       11. The method according to  claim 8 , wherein the step of stabilising at least one of a side wall of the first container and a second container comprises the step of inserting at least one flexible wall surface support member into the second dual-container mould cavity and making the at least one flexible wall surface support member contact a relevant region or regions of interior surfaces of the stretch-blow moulded integral dual-container. 
     
     
       12. The method according to  claim 8 , wherein said relevant surface region is the connection region between mouth opening zones of the first container and second container. 
     
     
       13. The method according to  claim 8 , wherein at least one flexible wall surface support member has a head-shape so shaped/formed in order to assist with the formation of the final inversion shape/form desired at the point of intersection of inverting and non-inverting walls. 
     
     
       14. The method according to  claim 1 , wherein at least one of said inversion pistons has a flat pushing face. 
     
     
       15. The method according to  claim 1 , wherein at least one of said inversion pistons has a fully profiled face that conforms to the final shape of the interior surface of the at least partial bottom wall of the second container to counteract inversion of the bottom wall of the second smaller. 
     
     
       16. The method according to  claim 11 , wherein during the step of inverting the at least one flexible wall surface support member and at least one of said profiled inversion pistons cooperate to stretchingly extend wall length of the inverted second container. 
     
     
       17. The method according to  claim 1 , further comprising, at any point in the production sequence, the additional step of cutting away one or more portions of the first container and/or one or more portions of the second container and/or one or more portions of the tubular blank. 
     
     
       18. The method according to  claim 1 , further comprising, at any point in the production sequence, the additional step of converting any one or more partially enclosed bottom walls into fully enclosed bottom walls. 
     
     
       19. The method according to  claim 18 , wherein the step of converting a partially enclosed bottom wall into a fully enclosed bottom wall comprises the step of forming a partially or fully enclosed air gap. 
     
     
       20. The method according to  claim 1 , further comprising, at any point in the production sequence, the additional step of further inverting any features or wall sections in either integrally connected container. 
     
     
       21. The method according to  claim 20 , wherein the step of further inverting any features or wall sections in either integrally connected container comprises the step of forming a partially or fully enclosed air gap. 
     
     
       22. The method according to  claim 1 , further comprising, at any point in the production sequence, the additional step of adding an additional part or parts of any shape or form to either integrally connected container. 
     
     
       23. The method according to  claim 22 , wherein the step of adding an additional part or parts of any shape or form to either integrally connected container comprises the step of forming a partially or fully enclosed air gap. 
     
     
       24. The method according to  claim 23 , further comprising, at any point in the production sequence, the additional step of adding additional material or materials of any form, property or nature into the air gap. 
     
     
       25. The method according to  claim 1 , further comprising, at any point in the production sequence, the additional step of applying additional shaping/forming methods to ensure that the inverted container fully assumes its final design shape/form. 
     
     
       26. The method according to  claim 1 , wherein the resulting double-walled container has a highly uniform average wall thickness significantly less than 0.35 mm, and preferably between 0.10 mm and 0.30 mm. 
     
     
       27. A stretch-blow moulding apparatus for producing a mechanically inverted double-walled container with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, the apparatus comprising:
 a first mould with a first mould cavity having a dual-container shape, designed for receiving a thermoplastic tubular blank with an open first end and an opposite second end, said cavity including a large-aperture recess for mechanical and/or sealing engaging-connection to the open end of the tubular blank, an engagingly connected first container cavity recess which includes a mouth opening zone, side wall zone(s) and a partially enclosed bottom wall zone, an engagingly connected second container cavity recess including a mouth opening zone, side wall zone(s) and a partially enclosed or fully enclosed bottom wall zone, with the first and second container cavity recesses extending in opposite directions from each other; 
 a second mould with a second mould cavity having a dual-container shape, designed for receiving said stretch-blow moulded integral dual-container, said second cavity including a large-aperture recess for mechanical and/or sealing engaging-connection to the partially enclosed bottom wall of said stretch-blow moulded first container, an engagingly connected first container cavity recess including a mouth opening zone, side wall zone(s) and a partially enclosed bottom wall zone, an engagingly connected second container cavity recess including a mouth opening zone, side wall zone(s) and a partially enclosed bottom wall zone, with the first and second container cavity recesses extending in opposite directions from each other, and at least one engagingly connected profiled inversion piston recess as part of the bottom wall of the second container cavity recess, and optionally including at least one heat-conditioning device for heating the first container or second container or both of the said stretch-blow moulded integral dual-container, and optionally including at least one pathway for interconnection with at least one below atmospheric air pressure source; 
 at least one profiled piston; 
 at least one wall stability device; and 
 a mechanical blank stretcher for mechanically stretching the tubular blank in a longitudinal axis direction when in a heat-conditioned condition; 
 the apparatus being adapted to perform the method of  claim 1 . 
 
     
     
       28. A stretch-blow moulding apparatus for producing a manually inverted double-walled container with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, the apparatus comprising:
 a first mould with a first mould cavity having a dual-container shape, designed for receiving a thermoplastic tubular blank with an open first end and an opposite second end, said cavity including a large-aperture recess for mechanical and/or sealing engaging-connection to the open end of the tubular blank, an engagingly connected first container cavity recess which includes a mouth opening zone, side wall zone(s) and a partially enclosed bottom wall zone, an engagingly connected second container cavity recess including a mouth opening zone, side wall zone(s) and a partially enclosed or fully enclosed bottom wall zone, with the first and second container cavity recesses extending in opposite directions from each other; 
 a mechanical blank stretcher for mechanically stretching the tubular blank in a longitudinal axis direction when in a heat-conditioned condition; 
 and may have at least one profiled piston; and 
 at least one wall stability device; 
 the apparatus being adapted to perform the method of  claim 1 . 
 
     
     
       29. The method according to  claim 1 , wherein the mechanical blank stretcher has heat-conditioning. 
     
     
       30. The method according to  claim 1 , wherein the second container is smaller than the first container and wherein after inversion the second container is internal to the first container. 
     
     
       31. The method according to  claim 1 , wherein the first container is smaller than the second container and wherein after inversion the first container is internal to the second container. 
     
     
       32. The method according to  claim 1 , wherein the first container is inverted and the second container remains at least substantially non-inverted. 
     
     
       33. The method according to  claim 1 , wherein the two dual-container shaped mould cavity set is a single dual-container shaped mould cavity set. 
     
     
       34. The apparatus as claimed in  claim 27 , wherein the two dual-container shaped mould cavity set is a single dual-container shaped mould cavity set.